A mitosome is an organelle found in some unicellular

eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

organisms, like in members of the supergroup

Excavata Excavata is a major supergroup of unicellular organisms belonging to the domain Eukaryota. It was first suggested by Simpson and Patterson in 1999 and introduced by Thomas Cavalier-Smith in 2002 as a formal taxon. It contains a variety of free- ...

. The mitosome was found and named in 1999, and its function has not yet been well characterized. It was termed a ''crypton'' by one group, but that name is no longer in use. The mitosome has been detected only in

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...

microaerophilic A microaerophile is a microorganism that requires environments containing lower levels of dioxygen than that are present in the atmosphere (i.e. < 21% O₂; typically 2–10% O₂) for optimal growth. A more r ...

organisms that do not have

mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...

. These organisms do not have the capability of gaining energy from

oxidative phosphorylation Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine tri ...

, which is normally performed by mitochondria. The mitosome was first described in ''

Entamoeba histolytica ''Entamoeba histolytica'' is an anaerobic parasitic amoebozoan, part of the genus ''Entamoeba''. Predominantly infecting humans and other primates causing amoebiasis, ''E. histolytica'' is estimated to infect about 35-50 million people worldwid ...

,'' an

intestinal parasite An intestinal parasite infection is a condition in which a parasite infects the gastro-intestinal tract of humans and other animals. Such parasites can live anywhere in the body, but most prefer the intestinal wall. Routes of exposure and infe ...

of humans. Mitosomes have also been identified in several species of

Microsporidia Microsporidia are a group of spore-forming unicellular parasites. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered protozoans or pr ...

and in ''

Giardia intestinalis ''Giardia duodenalis'', also known as ''Giardia intestinalis'' and ''Giardia lamblia'', is a flagellated parasitic microorganism of the genus ''Giardia'' that colonizes the small intestine, causing a diarrheal condition known as giardiasis. The ...

''.

Origin and function

Mitosomes are almost certainly derived from mitochondria. Like mitochondria, they have a double membrane and most proteins are delivered to them by a targeting sequence of amino acids. The targeting sequence is similar to that used for mitochondria and true mitochondrial presequences will deliver proteins to mitosomes. A number of proteins associated with mitosomes have been shown to be closely related to those of mitochondria or

hydrogenosome A hydrogenosome is a membrane-enclosed organelle found in some anaerobic ciliates, flagellates, and fungi. Hydrogenosomes are highly variable organelles that have presumably evolved from protomitochondria to produce molecular hydrogen and ATP i ...

s (which are also degenerate mitochondria). Current knowledge indicates mitosomes probably play a role in Fe-S cluster assembly, since they do not display any of the proteins involved in other major mitochondrial functions (

aerobic respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

haem biosynthesis Heme, or haem (pronounced / hi:m/ ), is a precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver. In biochemical terms, heme is a coordination complex "consisti ...

) and they do display proteins required for Fe-S cluster biosynthesis (like

frataxin Frataxin is a protein that in humans is encoded by the FXN gene. It is located in the mitochondrion and Frataxin mRNA is mostly expressed in tissues with a high metabolic rate. The function of frataxin is not clear but it is involved in assemb ...

cysteine desulfurase Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, somet ...

Isu1 Iron-sulfur cluster assembly enzyme ISCU, mitochondrial is a protein that in humans is encoded by the ''ISCU'' gene. It encodes an iron-sulfur (Fe-S) cluster scaffold protein involved in 2Fe-2S_cluster">2Fe-2S.html" ;"title="2Fe-2S_cluster.html ...

and a mitochondrial

Hsp70 The 70 kilodalton heat shock proteins (Hsp70s or DnaK) are a family of conserved ubiquitously expressed heat shock proteins. Proteins with similar structure exist in virtually all living organisms. Intracellularly localized Hsp70s are an import ...

). Unlike mitochondria, mitosomes do not have

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

s within them. The genes for mitosomal components are contained in the nuclear genome. An early report suggested the presence of DNA in this organelle, but more recent research has shown this not to be the case.

References

{{Self-replicating organic structures, state=collapsed Organelles